This application claims the benefit of Korean Patent Application No. 10-2004-0040314, filed on Jun. 3, 2004, in the Korean Intellectual Property Office, which is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of the Invention
The present invention relates to a solar cell and a method of manufacturing the same, and more particularly, to a dye-sensitized solar cell using an electrochemical principle and a method of manufacturing the same.
2. Description of the Related Art
A dye-sensitized solar cell is a photoelectrochemical solar cell using an oxide semiconductor electrode including photosensitive dye molecules capable of absorbing visible rays to produce electron-hole pairs and titanium oxide which transfers the produced electrons.
FIG. 1 is a schematic diagram of a dye-sensitized solar cell. The dye-sensitized solar cell includes a first electrode 1, a second electrode 2, and a porous membrane 3 having dyes 5 adsorbed thereto and an electrolyte 4 wherein the porous membrane 3 and the electrolyte 4 are provided between the first electrode 1 and the second electrode 2.
In a conventional silicon solar cell, absorption of solar energy and production of an electromotive force by separating electron-hole pairs occur at the same time. Meanwhile, in the dye-sensitized solar cell, absorption of solar energy and transfer of charges occur at different times. Specifically, dyes absorb solar energy and a semiconductor transfers charges of the absorbed solar energy.
Referring to FIG. 1, photons from incident sunlight are absorbed by the dyes 5. The excited dyes then send electrons to the porous membrane 3, which is composed of transition metal oxide. The electrons migrate via the first electrode 1 to an external circuit to transfer electrical energy, and subsequently enter the second electrode 2 with an energy state lowered correspondingly with the energy lost during migration.
The resulting holes of the dyes 5 are supplemented with electrons from the electrolyte 4 as the electrolyte 4 accepts electrons from the second electrode 2.
Even though such a dye-sensitized solar cell can be inexpensively manufactured and is environmentally friendly and flexible compared to the conventional silicon solar cell, it is not practical because it has a low energy conversion efficiency.
In solar cells, the energy conversion efficiency, i.e., the photoelectric conversion efficiency, is proportional to the number of electrons produced by absorption of sunlight. Therefore, to increase the energy conversion efficiency, the number of electrons generated may be increased by increasing the amount of sunlight absorbed, increasing the amount of the dye adsorbed, or reducing/preventing a loss of the produced electrons due to the electron-hole recombination process.
To increase the amount of the dye absorbed per unit area, a method of preparing nanoparticles an oxide semiconductor has been developed. To increase the amount of sunlight absorbed, a method of increasing the reflectance of a platinum (Pt) electrode and a method of preparing oxide semiconductor particles mixed with oxide semiconductor light scattering particles having a size of several μm have been developed.
However, such conventional methods have poor photoelectric conversion efficiency. Thus, a new technology for improving the photoelectric conversion efficiency is needed.
Meanwhile, the dye-sensitized solar cell illustrated in FIG. 1 has interfaces or regions that deteriorate its characteristics, such as an absorption ability or ability to transfer of solar energy charges. Such interfaces include, for example, an interface between the transition metal oxide particles of the porous membrane 3 and the electrolyte 4 and an interface between the first electrode 1 to which the porous membrane 3 is applied and the electrolyte 4.
In the interface between the transition metal oxide particles of the porous membrane 3 and the electrolyte 4, the electrons transferred from the dyes 5 to the transition metal oxide particle react with oxide iodine ions in the electrolyte 4, which decreases the concentration of electrons to be transferred to the electrode 2, thereby deteriorating an open circuit voltage Voc, a short circuit current Isc, and a fill factor FF of the solar cell.
The interface between the first electrode 1 to which the porous membrane 3 is applied and the electrolyte 4 can affect a charge collection property, which is based on a recombination rate and a collection rate. The recombination rate is attributed to a reduction in the number of reactions between electrons in the first electrode 1 and oxide iodine ions in the electrolyte 4. Thus, it is very important to reduce the number of recombinations occurring in the interface and to increase the collection rate of electrons in the solar cell in order to improve the characteristics of the solar cell.